DNA Replication Activity: Step-by-step guide to understanding how DNA duplicates itself during cell division.

Let's solve this DNA Replication Activity step by step. Since I can't see the image directly, I will interpret and complete the activity based on the text you've provided.

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🔬 BIO 141: DNA Replication Activity

We are given a parent DNA molecule, which is split into two strands during replication. Each strand serves as a template for a new complementary strand, resulting in two daughter DNA molecules (semi-conservative replication).

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## ✔ Step 1: Understanding the Components

Identification Key:

- P = Phosphate (backbone)
- D = Deoxyribose sugar (backbone)
- A = Adenine
- C = Cytosine
- T = Thymine
- G = Guanine

> Base pairing rules:
> - A pairs with T
> - C pairs with G

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Parent DNA Molecule (Given):

```
Left Strand (Top): P D C D P D G D P D A D P D G D P D T D
↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
(Base) C G A C T G A C T G T A C G T A C G T A

Right Strand (Bottom): P D G D P D C D P D T D P D C D P D A D
↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
(Base) G C T G A C G T A C A T G C A T G C A T
```

Wait — actually, the parent molecule is shown vertically in columns. Let’s reformat it properly from the table:

The parent molecule has two strands, each composed of alternating P-D (phosphate-deoxyribose) units, with bases in between.

Let’s extract the sequence of bases from the parent molecule:

#### Left Strand (Top):
From top to bottom:
- C
- G
- A
- T
- G
- T

So sequence: C-G-A-T-G-T

But wait — let's look at the full structure carefully.

Actually, the parent molecule is written in columns, with each column being a nucleotide:

| P | D | C | D | P | D | G | D | P | D | A | D | P | D | G | D | P | D | T | D |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| P | D | G | D | P | D | C | D | P | D | T | D | P | D | C | D | P | D | A | D |

So the top strand (left side) has bases:
C, G, A, T, G, T → But wait — looking at the alignment:

Each pair is:
- Top: C, G, A, T, G, T
- Bottom: G, C, T, A, C, A

Wait — let’s go row by row.

Looking at the Parent DNA Molecule box:

It has 6 rows, each with:
- P, D, [base], D, P, D, [base], D, ... etc.

So each row represents one nucleotide on each strand.

Let’s list them:

| Row | Top Strand (5' → 3') | Bottom Strand (3' → 5') |
|-----|------------------------|--------------------------|
| 1 | C | G |
| 2 | G | C |
| 3 | A | T |
| 4 | T | A |
| 5 | G | C |
| 6 | T | A |

So the parent double helix is:

```
Top (5' → 3'): C - G - A - T - G - T
Bottom (3' → 5'): G - C - T - A - C - A
```

Wait — that doesn’t make sense because base pairing must be correct.

Let’s check:

- C pairs with G → OK
- G pairs with C → OK
- A pairs with T → OK
- T pairs with A → OK
- G pairs with C → OK
- T pairs with A → OK

Yes! So the parent DNA is:

```
5' - C G A T G T - 3'
3' - G C T A C A - 5'
```

Now, during replication, the two strands separate, and each acts as a template.

---

## ✔ Step 2: Fill in the Daughter DNA Molecules

After separation, each strand becomes a template for a new complementary strand.

Left Daughter Molecule:

- Template: Original top strand: 5'-C G A T G T-3'
- New strand: synthesized in 5'→3' direction, complementary to this template.

Complementary to 5'-C G A T G T-3' is 3'-G C T A C A-5', but since we write sequences 5'→3', we reverse it: 5'-A C T A G C-3'

Wait — let’s do this carefully.

Template strand (top):
5' - C G A T G T - 3'

New strand (bottom) must be:
3' - G C T A C A - 5'

But when drawing the daughter molecule, we write the new strand in the same orientation as the original.

So the left daughter molecule consists of:
- Original top strand: 5'-C G A T G T-3'
- New bottom strand: 3'-G C T A C A-5' → written as 5'-A C A T G C-3'? No.

Wait — the new strand is built complementary and antiparallel.

So:

- Original top strand: 5'-C G A T G T-3'
- New strand (on bottom): 3'-G C T A C A-5'

So when we write the daughter molecule, we have:

```
Daughter 1:
5' - C G A T G T - 3'
3' - G C T A C A - 5'
```

But wait — no! The original bottom strand is now the template for the right daughter molecule.

Let’s clarify.

After splitting:

- Left half:
- Template: original top strand (5'-C G A T G T-3')
- New strand: 3'-G C T A C A-5' → so written as 5'-A C A T G C-3'? Wait, reverse.

Actually, the new strand is synthesized 5'→3', so it grows in the 5'→3' direction.

So if the template is 5'-C G A T G T-3', then the new strand is built from 3' to 5' relative to the template? No.

Better: The new strand is antiparallel and complementary.

So:
- Template: 5'-C G A T G T-3'
- New strand: 3'-G C T A C A-5'

So in the daughter molecule, we write:
```
5' - C G A T G T - 3'
3' - G C T A C A - 5'
```

But that’s just the original molecule!

No — wait, after replication, the original top strand remains, and a new bottom strand is made.

So the left daughter molecule is:

- Original top strand: 5'-C G A T G T-3'
- New bottom strand: 3'-G C T A C A-5'

Similarly, the right daughter molecule uses the original bottom strand as template.

Original bottom strand: 3'-G C T A C A-5'

So its complement is: 5'-C G A T G T-3'

So the right daughter molecule is:

- Original bottom strand: 3'-G C T A C A-5'
- New top strand: 5'-C G A T G T-3'

Therefore, both daughter molecules are:

Left Daughter:

```
5' - C G A T G T - 3'
3' - G C T A C A - 5'
```

Right Daughter:

```
5' - C G A T G T - 3'
3' - G C T A C A - 5'
```

Wait — they are identical?

Yes! Because the original molecule was:

```
5' - C G A T G T - 3'
3' - G C T A C A - 5'
```

After replication:
- One daughter has original top + new bottom
- Other has original bottom + new top

But the sequences are identical in both daughter molecules.

So both daughters are identical to the original molecule.

But let’s confirm:

- Original: 5'-CGATGT-3' / 3'-GCTACA-5'
- Daughter 1: 5'-CGATGT-3' / 3'-GCTACA-5' → same as original
- Daughter 2: 5'-CGATGT-3' / 3'-GCTACA-5' → same

So yes, both daughter molecules are identical to the parent.

But wait — only if the original was symmetrical? Actually, no, because the new strands are complementary.

Let’s write the actual nucleotides in the daughter molecules.

We need to fill in the Daughter DNA Molecules tables.

---

## ✔ Step 3: Fill in the Daughter Molecules Tables

Each daughter molecule has 6 nucleotides per strand.

Left Daughter Molecule:

- Template: original top strand: 5'-C G A T G T-3'
- New strand: complementary, antiparallel → 3'-G C T A C A-5'

So the new strand is added to the bottom of the left daughter.

In the table:

```
Left Daughter:
P D C D P D G D P D A D P D G D P D T D
P D _ D P D _ D P D _ D P D _ D P D _ D
```

Wait — the format is:

Each row is: P D [base] D P D [base] D ...

So we need to fill in the bases for the new strand.

For the left daughter, the new strand is:
- Complementary to: C, G, A, T, G, T
- So: G, C, T, A, C, A

And it goes in the bottom strand.

So the left daughter:

| P | D | C | D | P | D | G | D | P | D | A | D | P | D | G | D | P | D | T | D |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| P | D | G | D | P | D | C | D | P | D | T | D | P | D | A | D | P | D | C | D |

Wait — the new strand is 3'-G C T A C A-5', so when writing from top to bottom, the first nucleotide is G, then C, then T, etc.

So in the bottom row of the left daughter:

- Bases: G, C, T, A, C, A

So:

```
Left Daughter:
P D C D P D G D P D A D P D G D P D T D
P D G D P D C D P D T D P D A D P D C D
```

Similarly, right daughter:

- Template: original bottom strand: 3'-G C T A C A-5'
- New strand: 5'-C G A T G T-3'

So the new strand is: C, G, A, T, G, T

So the top row of right daughter gets these bases.

Right daughter:

```
P D C D P D G D P D A D P D G D P D T D
P D _ D P D _ D P D _ D P D _ D P D _ D
```

Wait — the top row is already filled with the original bottom strand? No.

Wait — in the diagram, the parent splits down the middle, and each half is used as a template.

So the left daughter has:
- Top: original top strand (C, G, A, T, G, T)
- Bottom: new strand (G, C, T, A, C, A)

The right daughter has:
- Top: new strand (C, G, A, T, G, T)
- Bottom: original bottom strand (G, C, T, A, C, A)

So the right daughter:

```
Top: C, G, A, T, G, T
Bottom: G, C, T, A, C, A
```

So in the table:

```
Right Daughter:
P D C D P D G D P D A D P D G D P D T D
P D G D P D C D P D T D P D A D P D C D
```

Wait — that’s the same as the left daughter?

No — let’s see:

In left daughter:
- Top: C, G, A, T, G, T
- Bottom: G, C, T, A, C, A

In right daughter:
- Top: C, G, A, T, G, T
- Bottom: G, C, T, A, C, A

So both daughter molecules are identical.

But that’s only because the parent had symmetric sequences? Let’s check:

Parent:
- Top: C G A T G T
- Bottom: G C T A C A

Is this palindromic? No.

But after replication, both daughters have:
- One strand: 5'-CGATGT-3'
- Other strand: 3'-GCTACA-5'

So yes, both daughter molecules are identical to each other and to the parent.

But wait — in reality, the parent is:
- 5'-CGATGT-3'
- 3'-GCTACA-5'

Each daughter has:
- One original strand + one new strand

But the new strands are complementary to the templates.

So:
- Daughter 1: original top + new bottom
- Daughter 2: original bottom + new top

But the sequences are:
- Daughter 1: 5'-CGATGT-3' / 3'-GCTACA-5'
- Daughter 2: 5'-CGATGT-3' / 3'-GCTACA-5'

So yes, identical.

But only because the new strands are exactly the same as the original ones.

So in this case, yes, the daughter molecules are identical.

---

## ✔ Step 4: Color Coding

According to directions:

- A = green
- T = yellow
- C = purple
- G = red
- P-O-P backbone = light blue (for parent), orange for new backbone

But since we’re not coloring here, we’ll just note the base colors.

---

## ✔ Step 5: Answer Questions

Question 1: Are the two daughter strands identical to the parent DNA molecule?

Answer:
Yes, each daughter DNA molecule is identical to the parent DNA molecule in sequence. This is because DNA replication is semi-conservative — each daughter molecule contains one original strand and one newly synthesized strand, but the overall sequence is preserved. In this case, the new strands are complementary to the templates, so the final duplexes are identical to the original.

> However, technically, the daughter molecules are not identical to the parent in terms of origin of strands, but structurally and sequentially, they are identical.

So answer: Yes, the two daughter molecules are identical to the parent molecule in sequence.

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Question 2: How much of the parent DNA molecule makes up one daughter DNA molecule?

Answer:
Half of the parent DNA molecule (one strand) makes up one daughter DNA molecule. Specifically, one original strand from the parent is conserved in each daughter molecule. The other strand is newly synthesized.

So: One-half (50%) of the parent DNA molecule (by strand) is present in each daughter molecule.

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Question 3: Summarize the process of DNA replication

Summary of DNA Replication:

1. Unwinding: The double helix of the parent DNA molecule is unwound by enzymes (like helicase), breaking hydrogen bonds between base pairs, creating two single strands.
2. Stabilization: Single-strand binding proteins stabilize the separated strands.
3. Primer Binding: Primase adds RNA primers to provide a starting point for DNA synthesis.
4. Elongation: DNA polymerase adds new nucleotides to each template strand, following base-pairing rules (A-T, C-G), synthesizing new strands in the 5' to 3' direction.
5. Antiparallel Synthesis: Because DNA polymerase only works in the 5'→3' direction, one strand (leading strand) is synthesized continuously, while the other (lagging strand) is made in fragments (Okazaki fragments).
6. Joining: DNA ligase joins the Okazaki fragments on the lagging strand.
7. Proofreading: DNA polymerase checks for errors and corrects mismatches.
8. Result: Two identical DNA molecules, each consisting of one original strand and one new strand — this is semi-conservative replication.

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## ✔ Final Answer Summary

Daughter Molecules Table Filled In:

Left Daughter Molecule:
```
P D C D P D G D P D A D P D G D P D T D
P D G D P D C D P D T D P D A D P D C D
```

Right Daughter Molecule:
```
P D C D P D G D P D A D P D G D P D T D
P D G D P D C D P D T D P D A D P D C D
```

> Note: Both are identical in sequence.

Color Key Application (if needed):

- A = green
- T = yellow
- C = purple
- G = red
- P-O-P backbone: light blue (parent), orange (new)

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✔ Answers to Questions:

1. Yes, the two daughter DNA molecules are identical to the parent molecule in sequence (semi-conservative replication).
2. One-half (50%) of the parent DNA molecule (one original strand) makes up each daughter molecule.
3. Summary: DNA replication involves unwinding the double helix, using each strand as a template to build a complementary strand, resulting in two DNA molecules, each with one old and one new strand.

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